A CS J = 5 → 4 Mapping Survey Toward High-Mass Star-forming Cores Associated with Water Masers

By Y. Shirley, N. Evans II, K. Young, C. Knez, D. Jaffe. 2003

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We have mapped 63 regions forming high-mass stars in CS J = 5 → 4 using the CSO. The CS peak position was observed in C34S J = 5 → 4 toward 57 cores and in 13CS J = 5 → 4 toward the nine brightest cores. The sample is a subset of a sample originally selected toward water masers; the selection on maser sources should favor sources in an early stage of evolution. The cores are located in the first and second Galactic quadrants with an average distance of 5.3 ± 3.7 kpc and were well detected with a median peak signal-to-noise ratio in the integrated intensity of 40. The integrated intensity of CS J = 5 → 4 correlates very well with the dust continuum emission at 350 μm. For 57 sufficiently isolated cores, a well-defined angular size (FWHM) was determined. The core radius (RCS), aspect ratio [(a/b)obs], virial mass (Mvir), surface density (Σ), and the luminosity in the CS J = 5 → 4 line (L(CS54)) are calculated. The distributions of size, virial mass, surface density, and luminosity are all peaked with a few cores skewed toward much larger values than the mean. The median values, μ1/2, are as follows: μ1/2 (RCS) = 0.32 pc, μ1/2 ((a/b)obs) = 1.20, μ1/2 (Mvir) = 920 M⊙, μ1/2 (Σ) = 0.60 g cm-2, μ1/2 (L(CS54)) = 1.9 × 10-2 L⊙, and μ1/2 (Lbol/Mvir) = 165 (L/M)⊙. We find a weak correlation between C34S line width and size, consistent with Δv ∼ R0.3. The line widths are much higher than would be predicted by the usual relations between line width and size determined from regions of lower mass. These regions are very turbulent. The derived virial mass agrees within a factor of 2-3 with mass estimates from dust emission at 350 μm after corrections for the density structure are accounted for. The resulting cumulative mass spectrum of cores above 1000 M⊙ can be approximated by a power law with a slope of about -0.9, steeper than that of clouds measured with tracers of lower density gas and close to that for the total masses of stars in OB associations. The median turbulent pressures are comparable to those in UCH II regions, and the pressures at small radii are similar to those in hypercompact H II regions (P/k ∼ 1010 K cm-3). The filling factors for dense gas are substantial, and the median abundance of CS is about 10-9. The ratio of bolometric luminosity to virial mass is much higher than the value found for molecular clouds as a whole, and the correlation of luminosity with mass is tighter.

Subfields: Astronomy and Astrophysics, Spectroscopy

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Citations in the corpus

Equilibrium Star Cluster Formation (2006, background): “Morphologies of Gas Clumps Shirley et al. (2003) observed CS (J = 5 → 4) emission from about 60 dense gas clumps containing high-mass star formation.”
Molecular Gas at High Redshift (2005, background): “Carbon monosulfide may be an even better tracer of dense, star-forming gas than is HCN (Shirley et al. 2003, but its weaker lines remain beyond the reach of present telescopes.”
STELLAR FEEDBACK IN MOLECULAR CLOUDS AND ITS INFLUENCE ON THE MASS FUNCTION OF YOUNG STAR CLUSTERS (2009, methodology): “In Figure 1, we plot Σ and Rh against M for starforming molecular clumps in the Milky Way, based on measurements of CS, C17O, and 1.2 mm dust emission in three independent surveys (Shirley et al. 2003; Faúndez et al. 2004; Fontani et al. 2005).”
THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES (2010, methodology): “ΣHCN is calculated using the mass contained within the FWHM size (RHCN) of the HCN gas, following the methods used in Shirley et al. (2003): ΣHCN = π −1 × ( Mvir M⊙ )( RHCN pc )−2 (M⊙ pc −2), (15) where Mvir is the virial mass enclosed in the source size at FWHM intensity.”
Connecting Dense Gas Tracers of Star Formation in our Galaxy to High-z Star Formation (2005, background): “The sample mapped in HCN J = 1− 0 is mostly a subset of a larger sample of Galactic massive dense cores that have been mapped in CS and dust emission (Shirley et al. 2003; Mueller et al. 2002).”
Slow Star Formation in Dense Gas: Evidence and Implications (2006, methodology): “…catalogmay not be complete over the region of sky it covers, there is probably at least some Galactic CS(5Y4) emission that is not correlated with water masers, and Shirley et al. (2003) only detect 75% of their targets in CS(5Y4), while they detect 90% in all the transitions for which they look.”
THE MOLECULAR GAS IN LUMINOUS INFRARED GALAXIES. II. EXTREME PHYSICAL CONDITIONS AND THEIR EFFECTS ON THE Xco FACTOR (2012, methodology): “A value of ǫg,∗∼500 (L⊙/M⊙) is actually measured in individual SF sites of spiral disks such as M51 and entire starbursts such as Arp 220 (Scoville 2003), while ∼(440 ± 100) (L⊙/M⊙) is obtained for CS-bright star-forming cores in the Galaxy (Shirley et al. 2003).”
WFCAM, Spitzer/IRAC and SCUBA observations of the massive star-forming region DR21/W75 - I. The collimated molecular jets (2006, background): “…with DR21/W75 have been estimated from modeling of dust continuum observations (Moore et al. 1991a; Chandler, Gear & Chini 1993a), molecular line maps (Dickel et al. 1978; Wilson & Mauersberger 1990) and, more recently, as virial masses from extensive CS observations (Shirley et al. 2003).”
RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION (2012, methodology): “…clear on what scale one should measure cloud properties: an entire GMC, with a mean density n ∼ 102 cm−3 obeying the Larson (1981) linewidth-size relation, a massive clump with a mean density n ∼ 105 cm−3 and a linewidth far above the Larson value (e.g. Shirley et al. 2003), or some other scale?”
Inverse dynamical population synthesis: Constraining the initial conditions of young stellar clusters by studying their binary populations (2012, background): “6 shows that the constraints compare well with masses and densities of molecular clumps that have just begun to form stars Mueller et al. (2002); Shirley et al. (2003); Fontani et al. (2005).”
THE LONG-TERM EVOLUTION OF THE GALACTIC DISK TRACED BY DISSOLVING STAR CLUSTERS (2010, background): “Observations of gas-dominated cluster-forming regions show column densities of ∼ 0.1 − 3 g cm−2 (Plume et al. 1997; Mueller et al. 2002; Shirley et al. 2003; Faúndez et al. 2004; Fontani et al. 2005); the data are summarized in Figure 1 of Fall et al. (2010).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “The properties of the Plume et al. (1992) sample have been studied in a series of papers (Plume et al. 1997; Mueller et al. 2002; Shirley et al. 2003), with the most recent summary in Wu et al. (2010a).”
Dusty Star Forming Galaxies at High Redshift (2014, background): “Interestingly, this is also true for massive, dense clumps in our galaxy (Shirley et al., 2003, and references therein).”
THE PROPERTIES OF MASSIVE, DENSE CLUMPS: MAPPING SURVEYS OF HCN AND CS (2010, methodology): “This result is similar to the result from CS 5-4 maps (the mean is 0.82 g cm−2, with a median of 0.60 g cm−2 (Shirley et al. 2003).”
On the Rapid Collapse and Evolution of Molecular Clouds (2007, methodology): “The highest-density value for ǫff in Krumholz & Tan (2007) comes from CS emission, and these authors suggest it is overestimated by a factor of a few because of undersampling in the CS surveys by Plume et al. (1997) and Shirley et al. (2003), who observed only H2O maser sources.”
Gravity or turbulence? Velocity dispersion–size relation (2010, methodology): “6), implies that massive, compact cores should develop larger velocity dispersions for larger column densities (N ∼ 1023–1025 cm−2, Shirley et al. 2003; Gibson et al. 2009; Wu et al. 2010).”
Toward Understanding Massive Star Formation (2007, background): “…have revealed dense cold clumps (molecular hydrogen density nH2 = 10 5 cm−3, gas temperature T = 10 – 20 K, diameter ∼ 0.5 pc) with gas masses ranging from a few hundred to a few thousand solar masses (Plume et al. 1997, Shirley et al. 2003, Garay et al. 2004, Motte et al. 2005, Evans 2005).”
THE LEGACY OF SCUPOL: 850 μm IMAGING POLARIMETRY FROM 1997 TO 2005 (2009, unknown): “…et al. (1993) N Curran et al. (2004, 2005) NGC 7538 SFR 81 2.8 Blitz et al. (1982) N Momose et al. (2001) Dotson et al. (2000) S157 SFR 82 2.5 Shirley et al. (2003) N Curran & Chrysostomou (2007) Cas A SNR 83 3.4 Reed et al. (1995) N Dunne et al. (2009) CB 244 BG 84 ∼0.180 Kun (1998) N…”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “It is about comparable to the mass function one obtains by selecting dense regions within molecular clouds (Shirley et al. 2003).”